Tree Exporter

Format-agnostic exporters for vcti trees: an Exporter protocol and a plugin catalog, with per-format writers as plugins.

vcti-tree-exporter defines what an exporter is and how to catalogue and look one up. It implements no file format itself — concrete writers (HDF5, JSON, CSV, NumPy, …) live in separate plugin packages and are registered by the consumer. The thing being exported is any vcti-tree tree whose node payloads are vcti-datanode DataNodes (data + attributes), so one tree can be written to any registered format without the producer knowing about serialization.

Cataloguing and lookup are built on vcti-plugin-catalog (Descriptor + Registry).

Installation

pip install vcti-tree-exporter

The base package is intentionally small. Install a format plugin for each format you need:

pip install vcti-tree-exporter-hdf5    # single .h5 file
pip install vcti-tree-exporter-json    # single .json document
pip install vcti-tree-exporter-npz     # single .npz archive
pip install vcti-tree-exporter-csv     # directory tree of CSV tables

Core concepts

Quick Start

Register the descriptors your application uses, then resolve one and write a tree:

from pathlib import Path
from vcti.tree.exporter.core import build_registry, get_exporter
from vcti.tree.exporter.hdf5 import get_exporter_descriptor as hdf5_descriptor
from vcti.tree.exporter.json import get_exporter_descriptor as json_descriptor

registry = build_registry([hdf5_descriptor(), json_descriptor()])
get_exporter(registry, "hdf5").export(tree, Path("model.h5"), overwrite=True)

registry is an ordinary vcti.plugincatalog.Registry, so the general way to select an exporter is to filter by attributes, then use the matching id — the same pattern as the rest of the ecosystem:

from vcti.lookup import Rule
from vcti.tree.exporter.core import EXTENSION_ATTR

(desc,) = registry.lookup.filter([Rule(EXTENSION_ATTR, "==", ".h5")])
desc.exporter.export(tree, Path("model.h5"))

Exporter ids are a small, fixed, well-known set, so using get_exporter(registry, "hdf5") directly is also fine.

Writing a format plugin

A plugin's exporter only has to satisfy the protocol — one export method, no base class — and ship a get_exporter_descriptor() factory carrying its metadata:

from pathlib import Path
from vcti.tree.exporter.core import EXTENSION_ATTR, FORMAT_ATTR, ExporterDescriptor

class JsonExporter:
    def export(self, tree, path: Path, *, overwrite: bool = False) -> None:
        ...   # walk the tree (node.name, node.attributes, node.load()), write JSON

def get_exporter_descriptor() -> ExporterDescriptor:
    return ExporterDescriptor(
        id="json", name="JSON Exporter", exporter=JsonExporter(),
        attributes={FORMAT_ATTR: "json", EXTENSION_ATTR: ".json"},
    )

Ship it in its own package (with its own format dependencies, e.g. h5py for HDF5). The consuming application decides which descriptors to register — there is no implicit global discovery.

Dependencies

• vcti-tree — the tree protocols the exporter reads.
• vcti-datanode — the node payload type.
• vcti-plugin-catalog — the Descriptor / Registry catalog.

(No heavy/runtime format dependencies live here — those belong to the per-format plugin packages.)